A traditional type computer is capable of having only a value of “0” or “1” for one bit. In contrast, a quantum computer can hold values of combination of “0” and “1” in an arbitrary ratio for one bit. With “n” pieces of quantum bits, “2n” pieces of states can be calculated in parallel. Such a quantum computer adopts quantum bits of nuclear spins, polarization of photons or the like, for example.
So far, quantum computers have been proposed using quantum bits described below (e.g., see Patent Literatures 1 to 3).    (1) Usage of nuclear magnetic resonance (usage of nuclear spin states)    (2) Usage of ion traps (usage of ionic electron states)    (3) Usage of quantum optics (usage of photon polarization)    (4) Usage of quantum dots (usage of states with different charge numbers)    (5) Usage of superconductor quantum bits (Usage of the number of magnetic fluxes or Cooper pairs)
Naturally, quantum bits used in quantum computers are required to have three properties described below.    (1) Quantum states being stable during calculation    (2) Variation of quantum states being controllable    (3) Large-scale integration being enabled